1. Field of the Invention
The invention generally relates to a windmill. More particularly, the invention relates to a tower type vertical axle windmill in which resistance blades (which are constantly perpendicular to the wind direction) and vertical blades are used to rotate an inertia flywheel to extract the energy from the wind. The windmill of the present invention is also called the wind tunnel type vertical axle windmill.
2. Description of the Prior Art
Humans have harnessed the wind power for thousands of years. Usually, blades (propellers) or flyball are used. In addition, a rotation speed enhancing device is also used to increase the rotation speed so as to drive a generator.
Please see FIGS. 11 and 12, which illustrate the traditional windmill. Such windmill has a horizontal or vertical axle and blades or flyball is used to drive the axle of a generator. The air flow cause the blades or flyball to rotate and the rotation may be converted to other mechanical form or be used to generate power.
The axle of the turbine of a horizontal axle windmill is parallel to the ground. Its sails may be adjusted according to the wind direction to extract the maximal amount of wind power. As of now, most of windmills are horizontal axle windmill. The disadvantages of horizontal axle windmill include loud noises and the fact that terrain winds and turbulences are difficult to overcome.
Either horizontal axle windmill or vertical axle windmill has the following disadvantages:                (1) Blades or flyball can harness only a part of the wind energy. The energy conversion efficiency is only 20 to 30% due to turbulences and the fact that blades are not facing against the wind direction.        
In addition, the actual energy conversion efficiency is further lowered after the rotational energy is converted into electricity.                (2) A bigger windmill is needed in order to generate more energy. The assembly and disassembly (for the purpose of maintenance) of such bigger windmill is difficult to do and cost is increased too.        (3) When there is strong wind, turbulences would be generated as the blades cut through the strong wind. When there is a super strong wind, the windmill has to stop its operation to avoid the damages of its components.        (4) Generally speaking, the higher the altitude is, the stronger the wind is. Therefore, preferably, windmills are installed at a high altitude. As the traditional windmills are made bigger and bigger, their weight and cost are increased and the difficulty in maintenance becomes greater too.        (5) Turbulences are most difficult to control and can cause serious damages. Most of the damages done on the blades have been caused by turbulences.        
As shown in FIG. 13, the blades of a wind turbine have a cross section similar to that of an airfoil. There are two main forces: a lifting force (U), which is perpendicular to the wind direction, and a resistance force (D), which is parallel to the wind direction. Such blade design has better aerodynamic properties.
In U.S. Pat. No. 7,413,404, a sail wing type windmill is disclosed to overcome the aforesaid disadvantages. It is a vertical axle windmill. Sail wings are used to extract energy from the wind. The angle of the sail wings may be adjusted to optimize the energy extraction. Therefore, such windmill has better performance.
As shown in FIG. 14, a negative pressure, F, would form behind the sail wings and such negative pressure works against the rotation of the axle and would adversely affect the performance of the windmill. In addition, in the aspect of orientation control, the cam may move out of the range in the X direction (please see FIGS. 7A and 7B). We can see that the sail wing type windmill has disadvantages and needs to be improved.
From the above, we can see that the windmills of the prior art have many disadvantages and need to be improved. To eliminate the disadvantages in the prior art, the inventor has put a lot of effort into the subject and has successfully come up with the tower type vertical axle windmill of the present invention.